Wide angle lenses have many advantages for CCTV and IP video surveillance. The first advantage is wide field of view (See images bellow). The second advantage is good low-light performance. And last but not least, wide angle lenses provide good depth of field as compared to telephoto lenses. However these advantages do come with a few drawbacks as well such as the possible geometrical distortion which appears as visible curvatures at the edges of a camera image and higher requirements for the camera resolution.
Hence it is important to maintain a proper balance between the wide field of view and possible drawbacks of wide angle lenses.
To find a proper focal length for wide angle lens, the CCTV designer needs to perform many calculations. To ease the lens selection the designer can use special 3D CCTV design software where you can clearly see all 3 parameters: actual field of view, lens distortions and camera resolution.